It's commonly known that a " flight idle" descent is the best for minimum fuel consumption.
The fact that the engines are producing a little, very little drag is good, the FMC can have the aircraft at cruise altitude and speed longer, therein saving fuel, and have the advantage of a very slightly steeper descent angle.
I guess you still use the old, tried and true, 3 times the altitude, in still wind for the TOD!
Further, when descending in moderate/heavy rain, I always put on a little power, aside from any anti-ice requirements, so as not to have a very much higher percentage of moisture than normal entering the fan.
At flight idle and reasonably high speeds, the slow running fan will force a percentage of the incoming airflow to bypass actually entering the fan, but, due to the forces involved, the momentum of the rain droplets will not allow them to change direction fast enough, and they enter the fan.
This increase in %age of water entering the fan can make the engine become unstable, and even flame out in extreme conditions, which is another reason to turn ON the engine anti-ice system, to unload the compressor, and increase your compressor stall margin.
Cheers